1. Field of the Invention
The present invention relates to a numerical control (NC) machining restart control system which when supplied with a machining restart command, automatically restarts numerically-controlled drilling of holes or the like which have been interrupted by something such as an electric power failure or a stop operation.
2. Description of the Prior Art
When drilling many holes or pockets (hereinafter referred to as holes or the like) in a workpiece through the use of a numerically-controlled machine tool, if the drilling operation is discontinued by some cause during drilling an arbitrary hole, it is customary in the prior art, when restarting the drilling operation, to re-execute an NC machining program from the very beginning, or to return the operation, by an operator's manipulation, to the block which was being executed when the drilling operation was interrupted and to restore various modal data for determining machining conditions. The modal data herein mentioned is one that, when contained in a block, is effective not only for that block but also for the subsequent ones until a cancel command is issued. The former method inevitably involves blank drilling of finished holes or the like, and hence waste much time, whereas the latter method involves a manual operation and often encounters difficulty in complete restoration of the modal data due to an erroneous manipulation.